1. Field of the Invention
This invention relates to a slide fastener of the discrete type in which a series of uniformly spaced fastener elements are mounted astride an inner beaded edge of each of oppositely disposed stringer tapes.
2. Prior Art
With reference to FIG. 3, a slide fastener 10' of this general type comprises a slider 14' having a pair of upper and lower wings (not shown) interconnected by a neck (not shown) located at its front end to define, together with a pair of guide flanges 18' formed along lateral edges of each of the upper and lower wings, a generally Y-shaped guide channel 22' through the slider for guiding the movement of the fastener elements 13' therethrough. The lengths of each pair of guide flanges 18' and the pitch of the fastener elements 13' have not been taken into consideration so that at least either of those two opposed fastener elements 13'c, located within the Y-shaped guide channel 22' in adjacent relation to the front end of the slider 14', are necessarily positioned with respect to the front ends 34' of the corresponding guide flanges 18' in the manner shown in FIG. 3 when the slider 14' is in its lowermost position. More specifically, the fastener element 13'c has its longitudinal axis A' disposed upwardly of the front ends 34' of the guide flanges 18'. When a lateral pull (indicated by arrow F') tending to separate the opposed stringer tapes away from each other is exerted on the slide fastener, the fastener element 13'c is pivoted or angularly moved in a counterclockwise direction about inner edges 36' of the front ends 34' of the guide flanges 18' which make contact with an end face 25' of the fastener element 13'c and serve as an axis of rotation. Thus, the end face 25' and the inner edges 36' function as the lever and fulcrum. Since the distance between the front side face 26' of the fastener element 13'c and the inner edges 36' is greater than the distance between the inner edges 36' and the rear side face 27', an inwardly directed force (indicated by arrow f'1) exerted on the outer rear corner 37' of the fastener element is substantially greater than an outwardly directed force (indicated by arrow f'2) exerted on the outer front corner 38' of the fastener element 13'c. The result is that even when the lateral pull F' is not so severe, the fastener element can easily be turned or angularly moved in a counterclockwise direction about the inner edges 36' representing the fulcrum to forcibly disengage the fastener element 13'c from the beaded tape edge 12'.